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(a) Schematic of the interventional multispectral photoacoustic imaging system and (b) a temporal sequence showing how triggering and pulse gating were performed using a digital control window.
Source publication
Precise device guidance is important for interventional procedures in many different clinical fields including fetal medicine, regional anesthesia, interventional pain management, and interventional oncology. While ultrasound is widely used in clinical practice for real-time guidance, the image contrast that it provides can be insufficient for visu...
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... optical parametric oscillator (OPO) system (VersaScan L-532, VersaScan L-532, GWU-Lasertechnik, Erftstadt, Germany) pumped by an Nd:YAG laser (repetition rate: 10 Hz; Quanta-Ray, INDI-40-10, Spectra-Physics, Santa Clara, California) was used as the PA excitation light source (Fig. 1). The OPO has two outputs: the signal (700 to 900 nm) and the idler (1100 to 2200 nm). Wavelength tuning was performed with a motorized crystal controlled by a custom Labview program (National Instruments, Berkshire, United Kingdom). The OPO outputs were focused onto separate silica-silica optical fibers with 910 μm cores (Thorlabs, ...
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... onto separate silica-silica optical fibers with 910 μm cores (Thorlabs, Newton, New Jersey) with achromatic doublet lenses (focal length: 50 mm; AC254-050-B, and AC254-050-C, Thorlabs). One of these two optical fibers directed light at an optical fiber of the same type, with its distal section positioned in the cannula of a 14 gauge needle (Fig. 1). Within tissue phan- toms and ex vivo tissue, the fiber tip was positioned 2 mm out of the needle tip to mitigate imaging artifacts from the metal nee- dle, including PA signal generation from the needle and US reverberations within the needle ...
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... detection [ Fig. 1(a)] was performed with a commer- cial US imaging system (SonixMDP, Analogic Ultrasound, Richmond, British Columbia, Canada) that was operated in its research mode. The system used a linear array imaging probe (L14-5/38, 128-element, 300 μm pitch, Analogic Ultrasound). Pre-beamformed channel data from the transducer element were sampled at ...
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... acquisitions of the US and PA images were triggered by light pulses. With the OPO operating continuously at 10 Hz, acquisitions were controlled by the Labview program via a dig- ital I/O card (NI-USB-6501, National Instruments). As illus- trated in Fig. 1(b), this scheme was realized using a logic AND gate (CD74HCT08E, Texas Instruments, Dallas, Texas) with two input signals: the optical trigger and the digital control window signal. The optical trigger was derived from an oscillo- scope (DPO3000, Tektronix, Oregon) with a photodiode signal as its input. The control window signal was 100 ...
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... blood vessel. The absorp- tion spectrum of the ink dilution was measured using a custom transmission spectrophotometer based on a visible near-infrared (NIR) spectrometer (Maya Pro, Ocean Optics, Milan, Italy). The measured absorption coefficient (μ a ) was 0.45 mm −1 at 800 nm, which is consistent with measurements of human blood. 25 As shown in Fig. 1(a), the US transducer and the ink tube were sur- rounded with 1% Intralipid dilution to simulate the optical scat- tering of biological tissues. 26,27 To avoid the confounding effects of PA excitation by the metal needle, a bare optical fiber was used to deliver excitation light. To estimate the imaging depth, the fiber was withdrawn ...
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... PA imaging was performed on fat and expired human blood cells (University College London Hospital Blood Transfusion Laboratory). Porcine fat was melted to tem- peratures in the range of 60 to 70°C and injected into a polymer tubing (inner diameter: 2.80 mm, outer diameter: 3.15 mm, Morcap56, Paradigm Optics, Vancouver) with a syringe [ Fig. 1(a)]. Red blood cells were injected into a second polymer tube. Prior to experiments, the RBCs were exposed to air. The oxygen saturation of these RBCs was estimated to be >90%. 31 The two polymer tubes were placed in parallel between two layers of chicken breast tissue. A 24 gauge needle was inserted through the chicken layers to ...
Citations
... Despite the advantages of PA and the prevalence of US-based modalities for obstetric applications, there is limited literature on the use of PA for placental imaging.While recent reviews have outlined emerging PA imaging clinical applications [10,14] and the development of novel PA contrast agents [17,19], this review takes a comprehensive look at the applications of PA imaging for placental monitoring. The article is subdivided into the three main areas of placental imagingvisualization of placental vasculature and anatomy [23][24][25], measuring functional information [26][27][28][29] such as placental oxygenation, and monitoring molecular features of the placenta [30,31]. ...
... Given the shallow depth achieved with PA systems, imaging human placental vasculature has been limited to excised ex vivo human tissues [23,24] and smaller animal models in vivo [25]. Maneas et al. [23] imaged superficial chorionic placental vessels using a Fabry-Perot-based planar sensor PA imaging (FP-PA) system. ...
... Moreover, scaling these systems to image humans is difficult, making FP-PA system impractical for clinical use. Xia et al. [24] developed a multiwavelength interventional PA imaging system for minimally invasive placental surgery. The light was delivered via a fiber positioned in the tip of a needle while US detection was simultaneously performed using a linear array transducer (L14-5/38) coupled with a SonixDAQ data acquisition system (Fig 1d-1f). ...
The placenta, a highly vascularized interface between the mother and fetus, undergoes dramatic anatomical and functional changes during pregnancy. These changes occur both during healthy development and adverse pathologies of pregnancy, such as preeclampsia. Abnormal placental development can lead to life-long health impacts on both the mother and child. Photoacoustic (PA) imaging, extensively developed for preclinical imaging applications in oncology and cardiovascular disease, uses optical energy to generate acoustic waves through thermoelastic expansion of light-absorbing chromophores within tissue. Recently, photoacoustic imaging has been used to study preclinical placental anatomy and function. If clinical translation of photoacoustic imaging of the placenta is achieved, the impact on maternal-fetal health could be expansive. This perspective highlights the recent progress in photoacoustic imaging for placental monitoring and discusses the progress needed for human clinical translation.
... The presence of the LEDs results in the PAI probe being bulkier than a regular ultrasound transducer, as seen in Before imaging began, blood-mimicking fluid was flushed through the vessels for contrast, using plastic tubing at either end of the vessel openings. The blood mimicking fluid was made up of India Ink diluted to 0.5%, as described by Xia et al. [116], which has an intrinsic absorption coefficient of 324 mm − 1 at 750 nm [133] and was found to be consistent with measurements of human blood [116,134]. This data was then transferred to a graphics processing unit (GPU) via a USB interface, and averaged across sequentially acquired PA images. ...
... The presence of the LEDs results in the PAI probe being bulkier than a regular ultrasound transducer, as seen in Before imaging began, blood-mimicking fluid was flushed through the vessels for contrast, using plastic tubing at either end of the vessel openings. The blood mimicking fluid was made up of India Ink diluted to 0.5%, as described by Xia et al. [116], which has an intrinsic absorption coefficient of 324 mm − 1 at 750 nm [133] and was found to be consistent with measurements of human blood [116,134]. This data was then transferred to a graphics processing unit (GPU) via a USB interface, and averaged across sequentially acquired PA images. ...
... It would also be interesting to explore the potential of the LED-based PAI systems to acquire different metrics such as oxygenation. Using multi-spectral imaging systems, it is possible to distinguish blood oxygenation levels [116,139], and it could be possible to replicate this in a phantom, by varying the contrast injected into the artery and veins. In addition, in future the phantoms described here could be characterised both optically and acoustically, so that there is greater information available on the properties of the phantoms used here, with their specific additives and freeze-thaw cycles. ...
In biomedical engineering, phantoms are physical models of known geometric and material composition that are used to replicate biological tissues. Phantoms are vital tools in the testing and development of novel minimally invasive devices, as they can simulate the conditions in which devices will be used. Clinically, phantoms are also highly useful as training tools for minimally invasive procedures, such as those performed in regional anaesthesia, and for patient-specific surgical planning. Despite their widespread utility, there are many limitations with current phantoms and their fabrication methods. Commercial phantoms are often prohibitively expensive and may not be compatible with certain imaging modalities, such as ultrasound. Much of the phantom literature is complicated or hard to follow, making it difficult for researchers to produce their own models and it is highly challenging to create anatomically realistic phantoms that replicate real patient pathologies. Therefore, the aim of this work is to address some of the challenges with current phantoms. Novel fabrication methods and frameworks are presented to enable the creation of phantoms that are suitable for use in both the development of novel devices and as clinical training tools, for applications in minimally invasive surgery. This includes regional anaesthesia, brain tumour resection, and percutaneous coronary interventions. In such procedures, imaging is of key importance, and the phantoms developed are demonstrated to be compatible across a range of modalities, including ultrasound, computed tomography, MRI, and photoacoustic imaging.
... Our method to assess the image resolution was inspired by an approach used in photo-acoustic imaging [237]. A 25 µm tungsten fibre (Quorum Technologies [235]. ...
In brain tumour resection, it is vital to know where critical neurovascular structuresand tumours are located to minimise surgical injuries and cancer recurrence. Theaim of this thesis was to improve intraoperative guidance during brain tumourresection by integrating both ultrasound standard imaging and elastography in thesurgical workflow. Brain tumour resection requires surgeons to identify the tumourboundaries to preserve healthy brain tissue and prevent cancer recurrence. Thisthesis proposes to use ultrasound elastography in combination with conventionalultrasound B-mode imaging to better characterise tumour tissue during surgery.Ultrasound elastography comprises a set of techniques that measure tissue stiffness,which is a known biomarker of brain tumours. The objectives of the researchreported in this thesis are to implement novel learning-based methods for ultrasoundelastography and to integrate them in an image-guided intervention framework.Accurate and real-time intraoperative estimation of tissue elasticity can guide towardsbetter delineation of brain tumours and improve the outcome of neurosurgery. We firstinvestigated current challenges in quasi-static elastography, which evaluates tissuedeformation (strain) by estimating the displacement between successive ultrasoundframes, acquired before and after applying manual compression. Recent approachesin ultrasound elastography have demonstrated that convolutional neural networkscan capture ultrasound high-frequency content and produce accurate strain estimates.We proposed a new unsupervised deep learning method for strain prediction, wherethe training of the network is driven by a regularised cost function, composed of asimilarity metric and a regularisation term that preserves displacement continuityby directly optimising the strain smoothness. We further improved the accuracy of our method by proposing a recurrent network architecture with convolutional long-short-term memory decoder blocks to improve displacement estimation and spatio-temporal continuity between time series ultrasound frames. We then demonstrateinitial results towards extending our ultrasound displacement estimation method toshear wave elastography, which provides a quantitative estimation of tissue stiffness.Furthermore, this thesis describes the development of an open-source image-guidedintervention platform, specifically designed to combine intra-operative ultrasoundimaging with a neuronavigation system and perform real-time ultrasound tissuecharacterisation. The integration was conducted using commercial hardware andvalidated on an anatomical phantom. Finally, preliminary results on the feasibilityand safety of the use of a novel intraoperative ultrasound probe designed for pituitarysurgery are presented. Prior to the clinical assessment of our image-guided platform,the ability of the ultrasound probe to be used alongside standard surgical equipmentwas demonstrated in 5 pituitary cases.
... Photoacoustic (PA) imaging has been of growing interest in the past two decades for its various potential preclinical and clinical applications, owing to its unique ability to resolve spectroscopic signatures of tissues at high spatial resolution and depths [21][22][23]. In recent years, several research groups have proposed the combination of US and PA imaging for guiding minimally invasive procedures by offering complementary information to each other, with US imaging providing tissue structural information and PA imaging identifying critical tissue structures and invasive surgical devices such as metallic needles [24][25][26][27]. Recently, laser diodes (LDs) and light emitting diodes (LEDs) have shown promising results as an alternative to solidstated lasers that are commonly used as PA excitation sources due to their favourable portability and affordability, which is of advantage to clinical translation [28][29][30]. ...
Photoacoustic imaging has shown great potential for guiding minimally invasive procedures by accurate identification of critical tissue targets and invasive medical devices (such as metallic needles). The use of light emitting diodes (LEDs) as the excitation light sources accelerates its clinical translation owing to its high affordability and portability. However, needle visibility in LED-based photoacoustic imaging is compromised primarily due to its low optical fluence. In this work, we propose a deep learning framework based on U-Net to improve the visibility of clinical metallic needles with a LED-based photoacoustic and ultrasound imaging system. To address the complexity of capturing ground truth for real data and the poor realism of purely simulated data, this framework included the generation of semi-synthetic training datasets combining both simulated data to represent features from the needles and in vivo measurements for tissue background. Evaluation of the trained neural network was performed with needle insertions into blood-vessel-mimicking phantoms, pork joint tissue ex vivo and measurements on human volunteers. This deep learning-based framework substantially improved the needle visibility in photoacoustic imaging in vivo compared to conventional reconstruction by suppressing background noise and image artefacts, achieving 5.8 and 4.5 times improvements in signal-to-noise ratio (SNR) and the modified Hausdorff distance (MHD) respectively. Thus, the proposed framework could be helpful for reducing complications during percutaneous needle insertions by accurate identification of clinical needles in photoacoustic imaging.
... In the past few years, forward-viewing PAE probes have attracted significant research interests, as they could be more convenient for use in various clinical applications such as optical biopsy and tumour margin assessment compared to side-viewing probes [22][23][24]. Moreover, a forward-viewing probe could also provide visualisation of critical tissue structures during minimally invasive procedures in clinical contexts including peripheral nerve blocks and foetal interventions [25][26][27]. With a PA microscopy implementation, a MEMS or a galvanometer mirror system was used to scan a focused laser beam at the proximal tip of a fibre bundle into individual cores, whilst the generated ultrasound (US) A-scans were received by a single-element ultrasound (US) transducer as reported in a study by Hajireza et al. [22]. ...
Multimode fibres (MMFs) are becoming increasingly attractive in optical endoscopy as they promise to enable unparalleled miniaturisation, spatial resolution and cost. However, high-speed imaging with wavefront shaping has been challenging. Here, we report the development of a video-rate dual-modal forward-viewing photoacoustic (PA) and fluorescence endo-microscopy probe with a high-speed digital micromirror device (DMD). Optimal DMD patterns were obtained using a real-valued intensity transmission matrix algorithm to raster-scan a 1.5 μm-diameter focused beam at the distal fibre tip for imaging. The PA imaging speed and spatial resolution were varied from ∼2 to 57 frames per second and from 1.7 to 3 μm, respectively. Further, high-fidelity PA images of carbon fibres and mouse red blood cells were acquired at unprecedented speed. The capability of dual-modal imaging was demonstrated with phantoms. We anticipate that with further miniaturisation of the ultrasound detector, this probe could be integrated into medical needles to guide minimally invasive procedures.
... 140 Similar studies of imaging depth were performed for PAI systems using interstitial light sources placed within the phantom or tissue. 68,100,115 These approaches demonstrate how the common diagonal tube array phantom design can be modified to suit different imaging system configurations. ...
Significance:
Photoacoustic imaging (PAI) is a powerful emerging technology with broad clinical applications, but consensus test methods are needed to standardize performance evaluation and accelerate translation.
Aim:
To review consensus image quality test methods for mature imaging modalities [ultrasound, magnetic resonance imaging (MRI), x-ray CT, and x-ray mammography], identify best practices in phantom design and testing procedures, and compare against current practices in PAI phantom testing.
Approach:
We reviewed scientific papers, international standards, clinical accreditation guidelines, and professional society recommendations describing medical image quality test methods. Observations are organized by image quality characteristics (IQCs), including spatial resolution, geometric accuracy, imaging depth, uniformity, sensitivity, low-contrast detectability, and artifacts.
Results:
Consensus documents typically prescribed phantom geometry and material property requirements, as well as specific data acquisition and analysis protocols to optimize test consistency and reproducibility. While these documents considered a wide array of IQCs, reported PAI phantom testing focused heavily on in-plane resolution, depth of visualization, and sensitivity. Understudied IQCs that merit further consideration include out-of-plane resolution, geometric accuracy, uniformity, low-contrast detectability, and co-registration accuracy.
Conclusions:
Available medical image quality standards provide a blueprint for establishing consensus best practices for photoacoustic image quality assessment and thus hastening PAI technology advancement, translation, and clinical adoption.
... When combined with existing optical engineering tools and the ability to miniaturize complete photoacoustic systems (e.g., catheter and endoscopy based photoacoustic imaging [30]), interest from surgeons and similar stakeholders has started to rise, as demonstrated by the number of authors with clinical affiliations rising from 5 in 2012 to 27 in 2020, based on the original research contributions referenced in Fig. 1. Additional optics-related advances include the flexible separation of light delivery systems from acoustic reception [31,32] and demonstrations of interstitial irradiation [33], bringing light as close to the surgical site as possible [34][35][36][37][38]. With external ultrasound reception, these advances enable deeper acoustic penetration depths, while maximizing optical penetration, effectively increasing the overall penetration depth of the technology over previous reports [39,40]. ...
... This novel approach was demonstrated in a phantom consisting of a fish heart embedded in chicken breast tissue, and photoacoustic imaging enabled improved visualization compared to ultrasound imaging of both the ground fish heart and the needle, with contrast improvements of 48% and 17%, respectively. Expanding this optical fiber-based approach, Xia et al. [32] demonstrated a multispectral photoacoustic imaging system by delivering excitation light ranging 750-900 nm and 1150-1300 nm from within the cannula of a needle. The system was evaluated in phantoms and ex vivo tissue demonstrating axial resolution of 100 µm and submillimeter depth-dependent lateral resolution. ...
Photoacoustic imaging–the combination of optics and acoustics to visualize differences in optical absorption – has recently demonstrated strong viability as a promising method to provide critical guidance of multiple surgeries and procedures. Benefits include its potential to assist with tumor resection, identify hemorrhaged and ablated tissue, visualize metal implants (e.g., needle tips, tool tips, brachytherapy seeds), track catheter tips, and avoid accidental injury to critical subsurface anatomy (e.g., major vessels and nerves hidden by tissue during surgery). These benefits are significant because they reduce surgical error, associated surgery-related complications (e.g., cancer recurrence, paralysis, excessive bleeding), and accidental patient death in the operating room. This invited review covers multiple aspects of the use of photoacoustic imaging to guide both surgical and related non-surgical interventions. Applicable organ systems span structures within the head to contents of the toes, with an eye toward surgical and interventional translation for the benefit of patients and for use in operating rooms and interventional suites worldwide. We additionally include a critical discussion of complete systems and tools needed to maximize the success of surgical and interventional applications of photoacoustic-based technology, spanning light delivery, acoustic detection, and robotic methods. Multiple enabling hardware and software integration components are also discussed, concluding with a summary and future outlook based on the current state of technological developments, recent achievements, and possible new directions.
... The value for real and imaginary part of PA signals are inversely proportional to each other [31]. It should be mentioned that phase value is corresponded to the amplitude of PA signal detected by transducer, wherein the higher the amplitude the more light absorption by absorber(s) within the medium [31,32]. ...
The aim of this study is to investigate the feasibility of using a laboratory assembled piezoelectric based photoacoustic (PA) system for noncontact monitoring fluid flow. This is to overcome the drawbacks of some existing fluid flow detection systems, which include expensive equipment and their maintenance cost, limited sensitivity and specificity in detecting signals from restricted regions or at low flow velocity. The produced PA signal waves detected by a piezoelectric transducer used in this study was processed to determine the required phase value (Ф), which value was found to correlate linearly with fluid flow status. The fluid pressure difference of 1.16 pascals (Pa) and 11.90 Pa applied to the developed mock circulatory system was observed to produce changes in phase value with mean ± standard deviation (SD) ΔФ of 0.79 ± 0.07 rad and 2.17 ± 0.07 rad, respectively, suggesting a linear response of the developed system with changes in circulation system. This trend was supported with the relatively low absolute difference of 0.07 ± 0.01 rad in the predicted values as compared to that of the ground truth. This work concluded that the capabilities and simplicity of the proposed PA system renders it feasible for cost effective, non-destructive assessment of fluid flow in future studies.
... The spatial divergence of commercially available high-power LED arrays (CYBERDYNE INC, Tsukuba, Japan) is approximately +/−60 • [28,29], which is acceptable in PAT where a relatively large illumination area is usually required. However, because of the large divergence and larger emission area (~1 mm 2 ), it is difficult to collimate the light and couple it to optical fibers for applications like minimally invasive PA imaging [9,[30][31][32]. In terms of eye/skin safety, high spatial divergence in combination with a low optical output makes LEDs a safer alternative to solid-state lasers for non-invasive PAI [20]. ...
Photoacoustic imaging is a hybrid imaging modality that offers the advantages of optical (spectroscopic contrast) and ultrasound imaging (scalable spatial resolution and imaging depth). This promising modality has shown excellent potential in a wide range of preclinical and clinical imaging and sensing applications. Even though photoacoustic imaging technology has matured in research settings, its clinical translation is not happening at the expected pace. One of the main reasons for this is the requirement of bulky and expensive pulsed lasers for excitation. To accelerate the clinical translation of photoacoustic imaging and explore its potential in resource-limited settings, it is of paramount importance to develop portable and affordable light sources that can be used as the excitation light source. In this review, we focus on the following aspects: (1) the basic theory of photoacoustic imaging; (2) inexpensive light sources and different implementations; and (3) important preclinical and clinical applications, demonstrated using affordable light source-based photoacoustics. The main focus will be on laser diodes and light-emitting diodes as they have demonstrated promise in photoacoustic tomography-the key technological developments in these areas will be thoroughly reviewed. We believe that this review will be a useful opus for both the beginners and experts in the field of biomedical photoacoustic imaging.
... The value for real and imaginary part of PA signals are inversely proportional to each other [31]. It should be mentioned that phase value is corresponded to the amplitude of PA signal detected by transducer, wherein the higher the amplitude the more light absorption by absorber(s) within the medium [31,32]. ...
The aim of this study is to investigate the feasibility of using a laboratory assembled piezoelectric based photoacoustic (PA) system for noncontact monitoring fluid flow. This is to overcome the drawbacks of some existing fluid flow detection systems, which include expensive equipment and their maintenance cost, limited sensitivity and specificity in detecting signals from restricted regions or at low flow velocity. The produced PA signal waves detected by a piezoelectric transducer used in this study was processed to determine the required phase value (Ф), which value was found to correlate linearly with fluid flow status. The fluid pressure difference of 1.16 pascals (Pa) and 11.90 Pa applied to the developed mock circulatory system was observed to produce changes in phase value with mean ± standard deviation (SD) ΔФ of 0.79 ± 0.07 rad and 2.17 ± 0.07 rad, respectively, suggesting a linear response of the developed system with changes in circulation system. This trend was supported with the relatively low absolute difference of 0.07 ± 0.01 rad in the predicted values as compared to that of the ground truth. This work concluded that the capabilities and simplicity of the proposed PA system renders it feasible for cost effective, non-destructive assessment of fluid flow in future studies.
